1. Field of the Invention
The present invention relates to a heat exchanger and a tube used in the same, provided in an air conditioner of a vehicle, or the like.
2. Description of the Related Art
Recently, tubes such as that shown in FIG. 7 have gradually come to be used in heat exchangers provided in air conditioners of vehicles, as a substitute for known extrusion-molded tubes. This tube shown in FIG. 7 is made by folding a plate in two so as to form a flat shape, and brazing the side edges of the plate together so as to form tube portion 1. A feature of this tube is the presence of dimples 3 formed from the outside of each of the opposed walls 2a and 2b, where the dimples protrude inside and two corresponding dimples from either wall side adhere to each other so that a plurality of column portions 4 are formed. Due to the column portions 4, turbulence of refrigerant occurs, thereby improving the heat-exchanging capability.
Due to the presence of the so-called xe2x80x9cdimplexe2x80x9d tube, the thickness of the tube wall can be thin because the tube portion is formed by folding a plate; thus, little material is necessary for manufacturing and the manufacturing cost is thus low, and as described above, a good heat-exchanging capability can be obtained because of the thin walls. In addition, the column portions 4 made of the dimples 3 are regularly arranged along the longitudinal direction of the tube, so that sufficient compressive strength (or pressure tightness) can be obtained even with the thin tube walls.
FIG. 8 shows a sectional view of a heat exchanger employing the dimple tube. In the figure, reference numerals 5 indicate dimple tubes, reference numeral 6 indicates a header having a hollow-cylindrical shape, and reference numerals 7 indicate cooling fins. An end of each dimple tube 5 is inserted inside the header 6 via tube insertion opening 6a. The inserted portion is fixed by brazing. The reason for using a hollow-cylindrical member (e.g., a pipe) as the header 6 is to secure the necessary compressive strength.
As explained above, the dimple tube is made by folding a plate in two and brazing the parts as necessary. The actual manufacturing of a heat exchanger does not employ a process in which the brazed dimple tube is inserted into the header and the inserted portion is again brazed so as to combine them. In the actual manufacturing process, a plate clad with a brazing filler metal is folded in two and inserted into the header, and after other portions such as cooling fins are also assembled, the assembled body is put into a heating furnace so as to braze each relevant portion.
Here, in the folded plate, the elastic force (or the like) of the plate may prevent the protruding portions of two dimples from adhering to each other. In order to solve this problem, the (shape of the) cooling fins is used, where the cooling fins and the tube plates are alternately arranged when they are attached to the header. Here, the elastic force of the cooling fins, between which the tube plates are placed, is used so as to make the corresponding protrusions of the dimples closely contact each other.
However, in the vicinity of the end of the dimple tube which is inserted into the header, the pressing force from the cooling fins may be insufficient. Accordingly, the corresponding protrusions do not closely contact each other and thus the brazing is incomplete, so that the necessary strength may not be obtained.
In consideration of the above circumstances, an objective of the present invention is to provide sufficient strength to a heat exchanger employing a dimple tube by improving the processing accuracy of the dimple tube and decreasing the processing error.
Therefore, the present invention provides a tube used in a heat exchanger, comprising a plate folded in two so as to make two edges of the plate contact each other and form a flat tube, wherein:
the plate comprises protrusions provided on each inner wall of the flat tube in a manner such that the heads of opposed protrusions on both the inner walls contact each other;
the plate is clad with a brazing filler metal and the protrusions are formed on a surface of the plate before the plate is folded, and the two edges of the plate and the heads of the opposed protrusions are respectively brazed after the plate is folded; and
a predetermined number of first sets of the opposed protrusions, positioned closest to the end of the tube, are larger than the other protrusions in a manner such that their size along the longitudinal direction of the tube is larger.
In the manufacturing of the heat exchanger, the force for making (i) the two edges of the plate and (ii) the heads of the opposed protrusions can be obtained by cooling fins, where the tubes and the cooling fins are alternately arranged with each other. According to the above structure in which the first sets of the opposed protrusions, positioned closest to the end of the tube, are larger than the other protrusions, the rigidity of the relevant end of the plate is improved, so that the pushing force from the cooling fins is transmitted from the middle area of the tube to the vicinity of the end portion of the tube, where the middle area receives sufficient pushing force from the cooling fins while the vicinity of the end portion originally receives less pushing force. Accordingly, the first sets of the opposed protrusions can closely contact each other. Therefore, the brazing filler metal spreads all over the heads of the opposed protrusions in the heating process and the heads are firmly brazed, thereby improving the joint strength.
Preferably, the width of each protrusion belonging to the first sets in a cross direction of the tube is substantially the same as the corresponding width of each of the other protrusions. Accordingly, the cross section of the passage in the area where the first sets of the protrusions are provided is substantially the same as the corresponding cross section of the passage in the area where the other protrusion are provided, so that an increase of pressure loss can be prevented at the relevant end of tube.
The present invention also provides a heat exchanger comprising:
a pair of headers, each having a plurality of tube insertion openings;
a plurality of tubes attached to the headers and arranged in parallel to each other, where both ends of each tube are inserted into the relevant tube insertion openings of the headers; and
cooling fins provided between the tubes arranged in parallel, and wherein:
each tube comprises a plate folded in two so as to make two edges of the plate contact each other and form a flat tube, wherein:
the plate comprises protrusions provided on each inner wall of the flat tube in a manner such that the heads of opposed protrusions on both the inner walls contact each other; and
the plate is clad with a brazing filler metal and the protrusions are formed on a surface of the plate before the plate is folded, and the two edges of the plate and the heads of the opposed protrusions are respectively made to contact by folding the plate, and wherein:
the assembled headers, tubes, and cooling fins are heated, and the two edges of the plate, the heads of the opposed protrusions, contact portions between the two ends of each tube and the headers, and contact portions between each tube and the cooling fins are respectively brazed; and
the cooling fins are arranged in a manner such that a predetermined number of first sets of the opposed protrusions which are positioned closest to the end of the tube directly receive a pushing force from the cooling fins.
Preferably, the first sets of the opposed protrusions are larger than the other protrusions in a manner such that their size along the longitudinal direction of the tube is larger.
In the above structure, the cooling fins are arranged between the tubes in a manner such that a predetermined number of first sets of the opposed protrusions which are positioned closest to the end of the tube directly receive the pushing force of the cooling fins; thus, the brazing filler metal spreads all over the heads of the opposed protrusions in the heating process and the heads are firmly brazed, thereby improving the joint strength.
According to the present invention, the joint strength of the folded plate portions is improved, thereby improving the compressive strength (or pressure tightness) at the relevant end of the tube.